Combined burst separator and color killer



Jan. 12, 1960 s. TARANTUR 2,921,123

COMBINED BURST SEPARATOR AND COLOR KILLER Filed Jan. 8, 1957 3 Sheets-Sheet 1 BYJ//f//%% l Hfs ATTORNEY Jan. 12, 1960 S. TARANTUR COMBINED BURST SEPARATOR AND COLOR KILLER Filed Jan. 8, 1957 3 Sheets-Sheet 2 TIME- P INVENTOR. 5am Taramur HIS ATTORNEY Jan. l2, 1960 s. TARANTUR 2,921,123

COMBINED BURST SEPARATOR AND COLOR KILLER Filed Jan. 8, 1957 3 Sheets-Sheet 3 I..- l l I l I l INVENTOR. ,Sam armzur HIS ATTORNEY.

p'roducing a color killer signal.

United States APatent j() i' lvSam Tarantur, River Grove, Ill., assigner -to Admiral Corporation, Chicago, Ill., a corporationv of Delaware Application January 8, 1957, Serial No. 633,073 6 Claims. (Cl. 178-5.4)

This vinvention relates, generally, to color television receiver circuits, and more particularly` to circuitry employing but a single tube and which is designed to eifect both the separation of the color .synchronizing signal vbursts (also referred to herein as color bursts) from the composite video signal and the production of 'a color killer control voltage for disabling the chrominance 'ircuitwhen a monochrome signal is being received.

In a simultaneous -type color television receiver curirently in use the picture information, in a general sense, ,'is supplied to Athe .image reproducing device through two different circuits. One of these circuits, known as the monochrome circuit, functions to `supply to the picture tbe a signal corresponding to 'the conventional black and white video signal, while the other circuit, lknown fasfthe chrominance circuit, functions to derive from the composite video signal the color signals which are also l'supplied to the picture tube to reproduce the color in `fthe picture. I n order to derive the color signals from fthe composite video signal it is lnecessary rst to derive "thecolor 'synchronizing signal Afrom information con- "t'ained in'the composite 4video signal. plished by. a third circuit means referred to herein as a 'color 'synchronizing circuit.v ADerivation of the color 'synchronizing' signal involves the separation of the color 'burstsifrorn the Vcomposite video signal. The color bursts arelo'cated'on the back porch of the composite video signal and having afrequency equal to some odd multiple nQfhalf'the line frequency. ln the Aprior art, `separation `offthe color ,bursts is accomplished by a gating-circuit Vwhich* functions `to pass konly the color bursts. These ,color 4bursts are then 'supplied to circuit means which responds thereto to `produce a continuous' wave color 'synchronizing signal of the proper phase and frequency. Another function of present day color television 're- "c'eivers is the production of a"co1orkiller voltage signal jwhich is employed when the received signal 'contains no kcolor information. Under such circumstances, there will be'riocolorbursts present ,in the composite video signal.

To prevent spurious signals from passing through the chrominance circuits and developing noise which will apj'pear ascolor in the monochrome picture, it is necessary :to disable'the chrominance'circuits. rThis can be done Aby cutting `offthe chroma amplifiers. t

` In theprior art, at least one tube has beenfemployed Y"to separate the 'color bursts from the video signal and 'at l'easttone other [tube has'been employed to respondto "theabsence of color bursts to produce the color killer signal which will cut off thechroma amplifier.

`lltjis van object ofthe present invention to perform the ":functionsof separating the color bursts and of producing au ycolor killer signal by a circuit employing 'but Va single tube. n l

p Another o bjectof the invention is vto provide an inexpensive circuit for separating the colorbursts 'and for Maira inject ofthenvemion is fo provide 'amiable This is accomn 2,921,123 Patented .J an. 12, 1960 Z circuit for separating the color bursts and for producing a color killer signal.

4A further object of the invention is the improvement of color television circuits, generally.

In accordance with the invention, there is provided an electron discharge device having a cathode, a control grid, and an anode. Grid leak circuit means, having 'a relatively long time constant compared to the time duration of a picture line, are provided to supply the Composite video signal to said control grid. Means are provided for supplying to the electron discharge device gating pulses which occur at times substantially coincident with the color bursts. The electron discharge 'device is responsive to these gating pulses to become conductive for the duration thereof. Other means are provided for supplying said gating pulses to said `control grid to cause the peak amplitude of the color bursts Ato lexceed the peak amplitude of the horizontal synchronizing pulses. Thus, the bias on the control grid will have two levels in accordance with the absence or presence Aof the color bursts. Integrating means are provided to integrate the output signal of the electron discharge'device to produce one of two D.C. output signal levels, in accordance with the particular level of bias on the control grid. The level of the D.C. output signal indicates the presence or theabsence of color bursts.

In accordance with a feature of the invention, there `can be employedin lieu of the grid leak circuit means, any voltage levelling circ 't which will produce on the control grid, abiasing potential whose magnitude varies in accordance with the ,presence or absence of the color bursts. Further, instead of the electron discharge device, other types of electronic valves, such as a transistor, for example,can be employed.

VThese and other objects and features of the invention `wil1 be more fully understood from the following detailed description thereof when read in conjunction vwith the drawings, in which: Y

Fig. 1 is a combination block diagram and schematic sketch of the invention;

Fig. 2 shows a representative composite video signal containing color bursts;

Fig. 3 is a curve representing the gating pulses;

Fig. 4 is a curve of the separated colo-r bursts;

Fig. 5 represents the sum of the curves of Figs. 2 and '73, 'and is the signal that is suppliedto the control grid t of the electron discharge device; and

Fig. 6 shows the relationship between the applied composite video color signal, the control grid bias, and the 'resultant plate current.

Referring now to Fig. 1, the block diagram portion thereof is priorart and is included in the specification primarily to Villustrate where and how the invention ts into the over-all system.

The invention, which functions to separate the color bursts from the composite video signal and also to produce a color killer voltage, is shown in schematic diagram vform within the broken line block 67.

The overall system will be discussed first. It is to be understood that such discussion will be general, since it is not a part of the invention, except insofar as gating pulses are derived therefrom. For a more detailed account of the system represented in Fig. l, reference is made to a publication entitled, LB-925 R.C.A. Developmental Color Television Receiver and published by the Radio [Corporation of America, RCA Laboratories Division, Industry Service Laboratory. The transmitted television signal is intercepted by the antenna 10, which supplies said signal to the tuner l11 and thence `to vthe intermediate'vfrequency(IF) amplifying section 12. `The "sound'channel *153 responds tothe output-of the IF amplifying section 12 to derive the audio signal which drives the speaker 14.

The output of the IF section 12 is also supplied to the Qvldeo secondY detector and to arstage of video amplification, both of which are included YWithin the block 15. From this point the signal is supplied tothe mixing matrix 23 through two different circuit paths, which are as follows: yThe first path is the luminance or monochrome circuit comprising video amplifier 16 and the delay line V17. yThe second path is the chrominance circuit including the band-pass amplifier 18, the chroma amplifier 19, the Q demodulating circuit 22, the I demodulating circuit 20, Vand the delay line 21. 'Ihe function of the chrominance circuit is to re-obtain the original I and Q voltages, the definitions of which are well known in the artand which are set forth in the RCA publication reCitedherenbeore. The I and Q voltages, and the monochrome signal, are supplied to the mixercircuit 23, where the original color signals are recbtained. The original color signals are then supplied in parallel through the red amplifier 24 and the D.C. restorer 91, the green amplifier 25 and the D.C. restorer 92, and the blue amplifier 26 and the VD.C. restorer 93, to the grids 64, 65, and 66, respectively, of the tri-gun kinescope 72, which also contains the three cathodes 61, 62, and 63. K For transmission purposes the color'subcarrier signal vwas removed from the I and Q signals, but must be `reinserted before the I and Q signals can be demodulated. To provide a reference signal for the reproduction of this color subcarrier signal is the function .of the color bursts. The color bursts are separated from the composite video signal by means of the present invention shown within the block 67, which will be deyscribed in more detail later. The separated color bursts Varethen supplied througha phase detector 27 and a reactance tube 28 to an oscillator 29. The phase and frequency of the output signal of the oscillator 29 are vaccurately controlled by the phase detector 27 and the ,reactance tube 28, which function in a well-known manner. More specifically, the output signal of the oscillator 29 and the color burst signal are compared in the |`phase detector 27 to produce a signal whose amplitude varies as the phase of the two signalsv varies. The 'reactance'tube 28 is responsive to the output signal of the phase detector to control the phase of the output signal of the oscillator 29. The oscillator output signal is supplied directly to the Q demodulator 22 and to the I demodulator through the 90 phase shift circuit 30.

Under some circumstances the receiver is employed to receive composite Video signals representative of black and white images. To prevent these monochrome signals Yfrom passing through the chrominance circuit and distorting the reproduced image, it has been found expedient to disable the chrominance circuit during the reception of monochrome signals. This is accomplished by supplying *a color killer signal to the chroma amplifier 19 through conductor 94 when no color bursts are present. Such a signal also is produced by the structure of the present invention, shown within the block 67.

The horizontal and vertical deflection signal generating circuits comprise the synchronizing signal separator 41 and the defiection signal generating circuits 43. 'Ihe out- Vput signals of block 43 are supplied to the vertical and horizontal windings 70 and 71.

Referring now specifically to the circuitry within the ,block 67, the composite video signal is supplied from the band-pass amplifier 18 to the controlV grid 52 of the pentode 50 through the coupling capacitor 47. 'Ihe Vpentode 50, which also comprises a cathode 51, a screen grid 53 biased by battery means 96, a grounded suppressor grid 54, and an anode 55, functions as a gate to separate the color synchronizing signal bursts from the applied composite video signal, and further functions i -As stated hereinbefore, the color killer superimposed produce a D.-C. output which is utilized as the color killer voltage.

The pulse forming circuit 42 is constructed to be responsive to the horizontal synchronizing pulses to produce gating pulses which are supplied to the anode 55 of the tube 50 through the coupling capacitor 44 and the tuned circuit 49. These gating pulses are represented by the typical pulse waveforms and 101 of Fig. 3 and can be seen to cause the pentode 50 to become conductive substantially during the period of the color burst signals, such as color bursts 102 and 103 shown in the curve of Fig. 2. The tuned circuit 49 is tuned to the frequency of the color synchronizing signal burst. Thus the output signal appearing across the tuned circuit 49 is a periodic burst of signal'having the same frequency and the same time duration as the color synchronizing signal bursts supplied to the control grid 52. Fig. 4 shows the output signal of the pentode 50. The winding 56 is inductively coupled to the tuned circuit 49 and functions to supply the output of the pentode 50 through the phase detector 27 and the reactance tube 28 to the oscillator 29, which is constructed to oscillate at a frequency near the frequency of the color synchronizing signal bursts. As discussed hereinbefore, the phase detector 27 and the reactance tube 28 function to lock the phase of the output Asignal of the oscillator 52 in exact synchronism with that of the color synchronizing signal burst.

In addition to separating the color bursts from the composite video signal, the circuit within the broken line blockY 67 functions to produce the color killer voltage.

voltage is employed, in the absence of color bursts, to cut off the chroma amplifier 19 and thus prevent monochrome signals from being supplied to the picture tube 72 via the chrominance circuit. When the color killer voltage is absent, the chroma amplifier will not be cut off and the chrominance circuit will function to supply the color signals to the picture tube. The color killer voltage signal is taken from the point 97 between the resistors 58 and 59, which form a voltage divider. It is to be noted that the D.C. potential at the point 97 need only have two levels; a first level, being the color killer voltage, and the second level, being a potential which will not disable the chroma amplifier. These two levels of potential are created in the following manner:

Under ordinary circumstances, the synchronizing pulses which constitute the most positive portion of the applied composite video signal would establish the amount of bias on the control grid 52 of pentode 50 through the action of the grid leak circuit comprising the capacitor 47 yand the resistor 48. However, the gating pulse supplied A to the anode 55 of pentode 'waveform of Fig. 5, in which the peak amplitude of the color bursts 104 and 105 exceed the amplitude of the horizontal synchronizing pulses 106 and 107. Thus, the bias on the grid 52 will be determined by the presence or absence of color bursts.

In Fig. 6 there is shown a plate current (ib) versus grid potential (eg) curve for the pentode 50 (Fig. 1). The waveform 131 represents a composite signal comprising the composite video signal and the gating signal thereon, said composite signal being supplied to the grid 52 and covering a time interval including several lines. The portions of the waveform 131, identied Vby reference characters 116, 117, 118, 119, 120,

series llinefs, More `Ispeciiically, "posit'e 'video signal Z:having color bursts 122, l123, '124,

130, 'whicharesuperimposed'upon thefcomposite video f signal in fmannerfdescribed =`hereinbefore. The PDlti'ons A4126 A127 'of "the waveform V131represent the Isuperimposed ygating pulses vduring periods when no "color 'synchronizing'signalbursts-'occun' o Fig. 6 also `shows the amount of bias on the grid 52 :aseies of color bursts occur, and whenjther'e are *no assume that `a comand 125 therein is supplied to the 'grid52 'of vthe pentode 50 of Fig. l. Because of theY action of the grid leak circuit (Figj 1) 'which willfunctiontocharge 'the capaci- `torl-"l, thetipslf-'thef-color burstsof-t'h'e composite video signal applied to the control grid 52'Ywil1 be levelled 'off at a potential just slightly more positive than the potential of the cathode 51. Thus, the bias on the control grid 52, which is represented by the broken line 132, will, after an initial few occurrences of the color burst, settle to a value as indicated, for example, between the times t1 and t2. If the color burst should be excluded from the composite video signal, as represented by the curve 132 between the times t3 and t4, the level of the grid bias will increase to a value as lndicated at about time t4. It can be seen that the magnitude of the control grid bias at time t2 is considerably greater than the magnitude of the grid bias at time t4. Thus, the value of the plate resistance of the pentode 50 at time t2 will be correspondingly greater than the value of the plate resistance at time t4. Consequently, the average D.C. potential appearing at the point 97 (Fig. l) will be higher at time t2 when the color signal bursts are present than when they are not present. The more negative level of the D.C. signal appearing at point 97 is employed to cut olf the chroma amplifier 19, whereas the more positive level will not disable the chroma amplifier. This creation of two D.C. potential levels at the point 97 will be more clearly understood with reference to the waveforms 110, 111, 112, 113, 114, and 134 of Fig. 6, which represent the output plate current of the pentode 50 that would ow if the pentode 50 were not gated. Only the solid line portions, however, of these waveforms, represent the signals that actually appear in the plate circuit of the pentode 50, since it is only during the corresponding intervals of time that the pentode is caused to become conductive by the gating pulses applied to the plate 55 thereof, as discussed hereinbefore. It is readily apparent that the waveforms 112 and 113, which contain the separated color bursts, have considerably less D.C. component therein than the waveform 134, which does not contain the separated color burst. Thus, the integration circuit (Fig. l), which comprises the capacitance 60 and resistors 58 and 59, functions to integrate the output signal of the pentode 50 to produce an average D.C. potential at the point 97 which is more negative in the absence of color bursts.

It is to be noted that the forms of the invention herein shown and described are but preferred embodiments of the same, and that various changes may be made therein without departing from the spirit or scope of the invention.

I claim:

1. In a color television receiver comprising a chroma channel and constructed to receive a composite video signal and also constructed to receive a composite chroma signal having horizontal synchronizing pulses and color synchronizing signal bursts occurring during the black level following each horizontal synchronizing pulse, means for separating the color synchronizing signal bursts from said composite chroma signal comprising an electron discolorfsignal bursts fora l "-6 *charge 1*device incl ding'aucatlrode, a control 'gridfand a'node, mean 'for supplying 'the composite :signal to said cor'itrfolj'gri'r aid means constructed to cooperate with the lrect'iier lforrrie'i *Isai'd control 'grid and said rcathode to `lievelt'he most :positive "i'ecycling peak amplitudes of the compositeuvideo signal at a potential slightly more positive vthan the Ipotential of said cathode, means for producing gating `pulses whichoccur during said color synchronizing signal'burs'ts, and means -for lsupplying said gating pulses 'to'saidcontrol grid `to cause the peak am- '.plitudeiofsaid color synchronizing signals toexceed vthe 'peak amplitude'ofsaid horizontalsynchronizing pulses, means for supplyingsaid gating pulses to said anode "of 'said lelectron discharge device to'cause said electron 'dis- `charge, device )to Abecome conductive for the duration thereof, rand 'means :for 'separating fthe D.C. component 'from' the'cutputsignal of the `electron discharge device, "said, iclir'rr'ra channel constructed and 'arranged tofbe 'responsive tothe TDi-C. component vof `the output "signal "of "the electron discharge `"device 'when "a" composite video signal is being supplied to said control grid to become non-operative.

2. In a color television receiver comprising a chroma channel, means for separating the color synchronizing signal bursts from an applied composite chroma signal and for creating a color killer voltage from an applied composite video signal, said means comprising an electron valve including an anode and a control electrode, voltage levelling means comprising grid leak resistor means connected to said control electrode and capacitor means for supplying said composite signal to said control electrode, means for generating gating pulses which occur during the color synchronizing signal bursts, means for supplying said gating pulses to said control electrode to cause the peak amplitude of the color synchronizing signal bursts to exceed the amplitude of the horizontal synchronizing pulses of the composite chroma signal, means for supplying said gating pulses to said anode to cause said electron valve to become conductive for the duration thereof, means for extracting that portion of the electron valve output derived from the color synchronizing signal bursts, and means for extracting the D.C. component of the output of said electron valve, said chroma channel constructed and arranged to respond to said D.C. component when a composite video signal is supplied to said control electrode to become non-operative.

3. Means for separating the color synchronizing signal bursts from the composite chroma signal and for creating a color killer voltage in accordance with claim 2, in which said means for extracting from the color synchronizing signal bursts from that portion of the electron valve output derived from the color synchronizing signal burst comprises a tuned circuit arranged in the output circuit of said electron valve.

4. In a television receiver having a chroma channel and adapted to receive a composite video signal and a composite chroma signal, said composite chroma signal including color synchronizing signal bursts occurring during the black level following each horizontal synchronizing pulse, means for separating the color synchronizing signal bursts during reception of said composite chroma signal and for developing a color killer voltage to disable said chroma channel during reception of said composite video signal comprising, a normally nonconductive electronic valve, means including said composite signals for establishing a rst bias level for said valve when said color synchronizing bursts are present and for establishing a second bias level for said valve when said color synchronizing bursts are absent, means for keying said valve to a conductive state only during the occurrence of said black level portion of said composite signal, the conduction current in said valve having a direct component of a first magnitude and an alternating component, when said color synchronizing bursts are present,

and a direct component of a second magnitude when said ycoupling means coupling `extremas color synchronizing bursts are absent, means responsive to the alternating component of said conduction current .for separating said color synchronizing bursts and means vresponsive to said second magnitude direct component of said conduction current for developing said color killer voltage.

5. In a color television receiver including a chroma channel, means for separating the color synchronizing bursts from an applied composite chroma signal and for developing a color killer voltage to disable said chroma channel when a composite video signal is applied comprising, an electronic valve having an input'circut and an output-circut, pulse means forl'generating voltage pulses at the line frequency of said composite signal, said composite signal to said input circuit, means for simultaneously applying said voltage pulses to said input circuit and to said output circuit substantially Vcoincidentwith the occurrencey of lvsaid color synchronizing burstson said composite signal, said pulses applied to saidroutput circuit initiating concolor-bursts are presentvand a said synchronizing color bursts are absent, and means in duction in said valve,'said input circuit including means second bias level when said outputV circuit for separating the alternating com- ,ponent of the conduction current in said valve from the direct component and for developing said color killer voltage when said valve is operated at said second bias level. Y

6. In a color television receiver as set forth in claim 5 wherein said means for developingsaidV color killer voltage is responsive to the magnitude'of said direct component of conduction current owing in said valve due to said second bias level.

References Cited in the tile of this patent `RCA Model 21-'CT-55, Service VData 1954, #T13, November 24, 1954. 

